Automatic control system for an air conditioning system



y 1966 w. v. MILLMAN 3,258,934

AUTOMATIC CONTROL SYSTEM FOR AN AIR CONDITIONING SYSTEM Filed Feb. 26, 1964 32 CONTROL LOOP HEAT EXCHANGE LOOP COM PRESSO R W EVAPORATOR 77 .1 TO PORTION 2a 5 OF CONTROL LOOP 5O 7O Q I TO SUCTION SIDE- OF CONTROL LOOP INVENTOR. WILLIAM V. MILLMAN ATTORNEY United States Patent 3,258 934 AUTOMATIC CONTROL SYSTEM FOR AN AIR CONDITIONING SYSTEM William V. Millman, Moline, Ill., assignor to American Air Filter Company, Inc., Jefferson, Ky., a corporation of Delaware Filed Feb. 26, 1964, Ser. No. 347,400 8 Claims. (Cl. 62-197) This invention relates generally to an automatic control arrangement for an air conditioning system, and in particular to an arrangement in which a pressurized refrigerant is used as the source of control power.

The principal object of the invention is the provision of a control arrangement and a refrigerating ssytem in which the control arrangement is self-contained in the sense that the source of control power is derived directly from the refrigerating system.

In accordance with the present invention, the refrigerating system includes the usual components including a refrigerant compressor, a condenser, an evaporator, and connecting refrigerant lines forming a heat exchange loop which may be used to cool the space being served, or in a reversed arrangement may be used as a heat pump to heat the space. A control loop in parallel with the heat exchange loop receives refrigerant from the compressor discharge and returns it to the suction side of the compressor. The control loop includes a first portion in which the pressure of the refrigerant is maintained at a predetermined, substantially constant differential with respect to the refrigerant pressure at the suction side of the compressor. Refrigerant from the first portion of the control loop is passed into a second portion of the control loop at a rate varying in accordance with variations in the condition in the space served by the system. A refrigerant flow restrictor separates the second portion of the control loop from the suction side of the compressor so that the pressure in the second portion is dependent, within limits, upon the relationship between the entrance and exit rates of refrigerant into and from the second portion. Control of the heat exchange loop components, or of other means affecting the conditioning of the space, is exerted in accordance with the differential in pressure between the second portion and the suction side of the compressor, or between the second portion and a downstream reference portion of the control loop which reflects the suction pressure of the compressor.

An embodiment incorporating the principles of the invention is shown in the accompanying drawing wherein:

FIGURE 1 is a schematic view of apparatus according to the invention; and,

FIGURE 2 is a sectional view of one type of actuator which may be used in connection with the invention.

FIGURE 1 is laid out with a refrigerating system of a generally conventional nature to the right of compressor 10, and the control arrangement to the left of the compressor. The refrigerating system includes, in addition to the compressor 10, a high side line 12 connected to the discharge of the compressor, a condenser 14, a receiver 16, an evaporator 18 having the usual expansion valve 20 in the line connected to the inlet of the evaporator, and a low side or suction line 22 connecting the outlet of the evaporator to the suction side of the compressor 10. The foregoing elements form what may be termed a heat exchange loop which may be used in the arrangement shown as a cooling system in which heat is extracted from the conditioned space by the evaporator. The description will proceed upon the basis that the heat exchange loop is to perform a cooling function for the space served but, as will be appreciated, the heat exchange loop may also be arranged as a heat pump in which case the served space is heated. In either case, the subject control arrangement may be used, it only being necessary that the compressor 10 be in operation.

As will be seen, the control loop to the left in FIG. 1 is in a parallel with the heat exchange loop and receives refrigerant from and returns it to the compressor 12. The pressure differential of the refrigerant between the high side and low side generated by the compressor varies with conditions of load, the type of refrigerant used, etc., so a pressure reducing valve 24 is provided in the high side line 12 to separate a first line portion 26 of the control loop from the high side line 12 connected to the discharge of the compressor. The pressure reducing valve 24 is connected through a sensing line 27 to the suction side of the control loop, and operates through a conventional spring and pressure balance system to maintain a refrigerant pressure in the first line portion 26 of the loop at a constant differential with respect to the reference pressure in the suction side or reference portion of the loop.

The denoted first portion 26 of the control loop is separated from a second or control portion 28 of the control loop by a condition responsive valve 30. For descriptive purposes, it may be assumed that valve 30 is responsive to a temperature condition, rather than some other condition, in the space being served. The sensing bulb or element 32 is of course located in the served space and varies the opening of the control valve 30 in accordance with variations in the condition sensed by the element. Preferably, and as is conventional, the control valve 30 is adjustable by an arrangement which permits regulating a spring force exerted in opposition to the pressure exerted by the charge in the sensing element 32.

The second portion 28 of the control loop is separated from the suction side or reference portion of the control loop by a restrictor 34 having an orifice sized to bleed refrigerant at a substantially constant rate in normal operation. With the described arrangement, it will be appreciated that a pressure increase will occur in the second or control portion 28 of the loop when refrigerant is being passed into the control portion at a faster rate than it is being bled through the restrictor 34, and a decrease in the pressure in the control portion 28 will occur when the refrigerant is being admitted to the control portion 28 at a rate less than it is bleeding through the restrictor 34 to the suction side of the system. To obtain an operation in which the refrigerant pressure differential can be increased or decreased, the orifice of the control valve 30 is sized in accordance with the orifice in the restrictor 34 so that refrigerant may be admitted to the control portion 28 at either a faster or slower rate than it is capable of passing through the restrictor 34.

The variable pressure diffrential existing between the second portion 28 and the suction side of the control loop is used to provide the variable force needed to operate actuator means. Such actuator means, designated 36 in FIG. 1, has one side connected to the control portion 28, and its other side connected to the reference portion designated 37. The reference portion 37 of course reflects the suction pressure at the compressor even though check valves or the like, as illustrated, may be in the line leading to the suction inlet of the compressor. The same differential pressure existing across the restrictor 34 is imposed across the actuator 36 and since refrigerant does not pass through the actuator, the differential pressure across it will rise and fall in accordance with the differential across the restrictor.

As is well known, control actuators can be used in a variety of Ways to affect the conditioning of the space served. For example, the actuator 36 may be used to exert control of the heat exchange loop by switching in a hot gas bypass circuit (not shown). Or it may be used to energize electrical resistance heaters, or to operate damper means varying the admission of outdoor air to the space being served, or to control the flow of .air over the evaporator or over the heating elements being used to heat or cool the space served. It will thus be appreciated that the exact manner in which the actuator means is used to vary the conditions in the space served is subject to great variation, and is not in itself part of the invention; however, for purposes of illustration, shaft 52 can be connected to a suitable control mechanism 38 by means of lever 39 which moves in response to movement of element 52 of actuator 36. Movement of element 52 directly operates control mechanism 38 which may include any suitable means for controlling the conditioning of the served space, including, but not limited to, the aforementioned methods. For purposes of the present example, control mechanism 38 can include an input power source 41 and an output power means 45 connected to elements (not shown) for conditioning the space to be served.

The structure of one type of actuator 36 is shown in FIGURE 2. It is in the general form of a cylinder 40 having opposite closed ends 42 and 44. The cylinder contains concentrically arranged elements including a large outer bellows 46, a biasing spring 48, a small inner bellows 50 and a reciprocatingly mounted operating rod 52 extending along the axis of the cylinder. The left end of rod 52 extends through a central opening of cylinder end 44, and the right end of the rod is provided with an axial bore 54 which receives a guide pin 56 carried by the right cylinder end 42. A disc 58 is mounted on the right end of the rod 52 by means of a nut 60 turned onto the threaded right end of the rod.

The outer bellows 46 is sealed at its left end to the cylinder structure and at its right end to the periphery of the disc 58 so that an outer chamber 62 is formed. Outer chamber 62 is sealed from the remainder of the interior of the actuator and is adapted to be placed in communication with the control portion 28 of the control loop through an inlet port 64 in the actuator cylinder.

The inner bellows 50 is sealed at its left end to the cylinder end 44 around the opening through which the operator rod 52 passes, and the right end of the inner bellows 50 is sealed to the right end of the operator rod 52 and the disc 58. Thus an inner annular chamber 66 is formed between the outer and inner bellows, and this inner chamber is adapted to be placed in communication with the suction side of the control loop through a port 68. The innermost annular space 70 formed between the inner surface of the inner bellows 50 and the outer surface of the rod 52 may be left open to atmosphere.

The spring 48 extends for the length of the inner chamber 66 with its left end bearing against the cylinder end wall 44 and its right end urging the disc 58 to the right. The force of the spring against the disc to the right is opposed by the pressure differential existing between the outer chamber 62 and the inner chamber 66 acting against the disc to move it toward the left. With the disc and operator rod 52 secured to each other, movement of the disc of course results in corresponding movement of the rod. An actuator construction including a bellows arrangement is presently preferred in that it eliminates any sliding seal arrangement which would be a potential source of refrigerant leakage. It will also be appreciated that with the described actuator construction, the bellows across which the greatest pressure differential exists is the inner bellows 50 which, as illustrated,.is provided with corrugations of small amplitude, and sections of short span separated by guide rings. ment, the inner bellows is structurally better able to tolerate the potentially high pressure differential between the chamber 66 [and the inner chamber 70 than the outer bellows 46. In that connection, the pressure differential between chamber 66 and atmosphere can fall in a range as high as say 250-300 p.s.i. when certain refrigerants are used (Refrigerant 22 for example) and high ambient tem- With the illustrated arrangeperatures exist around the actuator with the system in a non-operating condition.

To insure proper operation of the control loop, the ambient temperature around it should be at least high as the temperature corresponding to the saturated pressure of the control pressure differential. For purposes of illustration, it will be assumed that Refrigerant 22 is being used, and a twenty pound differential is maintained between the first portion 26 and the suction side of the control loop. With the evaporator 18 operating at 40 F. (about 69 p.s.i.g.), then the ambient temperature of the control loop should be at least 53 F. (89 p.s.i.g.) to prevent condensation of the refrigerant in the control loop. As will be apparent from the example, this does not usually pose a problem since the temperature of the control loop will normally be sufficiently high with respect to the saturated pressure of the refrigerant that condensation is avoided. However, in any unusual application of the refrigerating system and con-trol arrangement wherein there is a possibility of depressed control loop temperatures, independent heating means such as electrical resistance heaters may be provided adjacent control loop elements to prevent refrigerant condensation in the control loop.

For explaining the general operation of the system, it will be continued to be assumed that the pressure reducing valve 24 is adjusted to provide a twenty p.s.i. differential between the first portion 26 and the suction side of the control loop. It will also be assumed that the heat exchange loop is operating to cool the space, and that the control valve 30 is responsive to variations in temperature of the space served by the heat exchange loop. With the valve 30 arranged to be direct-acting, a decrease in temperature of the space results in the valve 30 moving toward a closed position; and upon an increase in temperature, the valve moves toward an open position. Accordingly, the difference in pressure between the second or control protion 28 of the loop and the suction side will vary in a range of 0-20 p.s.i. depending upon the valve position, which in turn depends upon space temperature.

With no pressure differential existing across the outer bellows 46 (between the outer chamber 62 and the inner chamber 66) the rod 52 will be in a position wholly determined by the spring 48 forcing the disc 58 to the right. With the maximum differential of 20 p.s.i., the force of the pressure to the left will overcome the force of the spring to the right, and the rod will assume a maximum leftward position. With intermediate pressures, the rod will take correspondingly intermediate positions. Thus, the operation of the actuator 36 is similar to the operation of conventional actuators, and the movement of the rod 52 is used to exert control on the means conditioning of the space. While the operational similarities are apparcut, it will be appreciated that the actuator and system according to the invention is such that refrigerant does not pass through the actuator, and the acutator is responding to the differential between two variable pressures.

The invention claimed is:

1. A space conditioning system including:

(a) a heat exchange loop, including a condenser and evaporator, for conditioning said space;

(b) a refrigerant compressor adapted to pump a refrigerrant through said heat exchange loop;

(0) a control loop connected to said refrigerant compressor in parallel with said heat exchange loop;

(d) means for reducing the pressure of said refrigerant in a first portion of said control loop to maintain a predetermined, substantially constant differential between the refrigerant pressure in said first portion and in a reference portion of said control loop refleeting the suction pressure of said compressor;

(e) means for varying the flow of refrigerant from said first portion into a second portion of said control loop in accordance with variations in condition in said space;

(f) refrigerant flow restriction means between said second portion and said reference portion of said control loop; and,

(g) means for controlling the conditioning of said space including control actuator means responsive to changes in the differential in pressure between said second portion and said reference portion of said control loop.

2. In a system according to claim 1:

(a) said control actuator means having one side connected to said second portion and an opposite side connected to said reference portion, said actuator including means preventing passage of refrigerant from said one side to said opposite side.

3. A space conditioning system including:

(a) a heat exchange loop, including a condenser, and

evaporator for conditioning a space to be served;

(a-l) a refrigerant compressor adapted to pump a refrigerant through said heat exchange loop;

(b) a control loop connected in parallel with said heat exchange loop to also receive refrigerant from the discharge side of said compressor and return said refrigerant to the suction side of said compressor;

(c) means for maintaining a predetermined, substantially constant, differential between the refrigerant pressure in a first portion of said control loop and the suction pressure of said compressor;

(d) means for varying the flow of refrigerant from said first portion of said control loop into a second downstream portion of said control loop in accordance with variations in conditions in said space served by said heat exchange loop;

(e) means for bleeding refrigerant from said second portion of said control loop back to the suction side of said compressor so that the differential in pressure between said second portion of said loop and the suction side of said compressor varies in accordance with the rate at which said refrigerant is passed from said first portion into said second portion;

(f) control actuator means connected to said second portion and to said suction side of said compressor and responsive to changes in the differential in pressure between said second portion and said suction side of said compressor; and

(g) control means responsive to said control actuator means for controlling conditioning of said space to be served.

4. In combination:

(a) refrigerating system, for conditioning a space, in-

cluding a compressor, a refrigerant, a condenser, and an evaporator forming a heat exchange loop;

(b) a control loop in parallel with said heat exchange loop for utilizing said refrigerant as a source of control power;

() pressure regulator means for maintaining a predetermined, substantially constant differential between the pressure in a first portion of said control loop and the suction side of said compressor;

((1) means responsive .to conditions in the conditioned space for varying the rate of refrigerant flow from said first portion into a second downstream portion of said loop;

(e) means restricting the rate of refrigerant flow from said second portion to the compressor suction side line of said loop to a value less than the rate at which refrigerant is capable of being admitted into said second portion of said loop;

(f) control actuator means responsive to the differential in refrigerant pressure between said second portion and the suction side of said compressor to operate control means for varying the conditioning of said space; and

(g) control means responsive to said control actuator means for controlling the conditioning of said space to be served.

5. An arrangement in which a pressurized refrigerant is used as a source of control power for affecting the conditioning of a space served by the refrigerating system from which said pressurized refrigerant is taken, said refrigerating system including:

(a) a compressor discharging said refrigerant at a higher pressure and receiving said refrigerant at a lower pressure;

(b) a control loop line having one end connected to the discharge side of said compressor and the other end connected to the suction side of the said com pressor, said line including,

(b-l) a first portion separated from said compressor discharge side by means for reducing the refrigerant pressure to values exceeding the pressure in a reference portion reflecting the suction pressure of said compressor by a predetermined differential,

(b2) a second portion separated from said first portion by means for varying the flow rate of refrigerant into said second portion in accordance with variations in the condition of the space being served,

(b-3) refrigerant flow restricting means separating said second portion from said reference portion; and

(c) control means, including control actuator means responsive to the difference in pressure between said second portion of said line and said reference portion, for actuating means for varying said condition in said space being served.

6. An arrangement in which a pressurized refrigerant is used as a source of control power for affecting the conditioning of a space served by the refrigerating system from which said pressurized refrigerant is taken, said refrigerating system including:

(a) a compressor discharging said refrigerant at a higher pressure and receiving said refrigerant at a lower pressure;

(b) a control loop line having one end connected to the discharge side of said compressor and the other end connected to the suction side of said compressor, said line including, in order from high side to low side of said compressor, a first portion, a second portion, and a reference portion,

(bl) said first portion being separated from said compressor by valve means reducing the refrigerant pressure in said first portion to values exceeding the refrigerant pressure in said reference portion by a predetermined constant differential,

(b-2) said first and second portion being separated by valve means responsive to temperature conditions in said space,

(b3) said second and said reference portions being separated by refrigerant flow restriction means; and

(c) control actuator means having opposite sides connected to said second and said reference portions, and sealed against flow theret-hrough, for actuating means for controlling the temperature control in said space in response to variations in the pressure differential between said second and said reference portions.

7. An arrangement according to claim 6 wherein:

(a) said temperature responsive valve means regulates the rate of refrigerant flow from said first to said second portion in a range bracketting the normal rate of refrigerant flow through said flow restriction means.

8. An automatic condition arrangement including:

(a) a refrigerant compressor connected to a heat exchange loop adapted to condition a space;

(b) a control loop having an inlet and outlet connected to the high side and low side respectively of said compressor;

(c) means reducing the refrigerant pressure in a first portion of said control loop to maintain a predetermined, substantially constant differential above the refrigerant pressure in a low side reference portion of said control loop;

(d) means varying the rate of refrigerant flow from said first portion into a second portion of said control loop in accordance with variations in condition in said space;

(e) refrigerant flow restriction means between said second portion and said reference .portion of said control loop;

(f) control actuator means responsive to variations in refrigerant pressure differential between said second portion and said reference portion of said control loop for regulating the conditioning of said space; and 1 (g) control means responsive to said control actuator means for controlling conditioning in said space.

References Cited by the Examiner UNITED STATES PATENTS 1,782,688 11/1930 Hoffman 62-200 2,454,263 11/1948 Newton 62--197 MEYER PERLIQN, Primary Examiner. 

1. A SPACE CONDITIONING SYSTEM INCLUDING: (A) A HEAT EXCHANGE LOOP, INCLUDING A CONDENSER AND EVAPORATOR, FOR CONDITIONING SAID SPACE; (B) A REFRIGERANT COMPRESSOR ADAPTED TO PUMP A REFRIGERANT THROUGH SAID HEAT EXCHANGE LOOP; (C) A CONTROL LOOP CONNECTED TO SAID REFRIGERANT COMPRESOR IN PARALLEL WITH SAID HEAT EXCHANGE LOOP; (D) MEANS FOR REDUCING THE PRESSURE OF SAID REFRIGERANT IN A FIRST PORTION OF SAID CONTROL LOOP TO MAINTAIN A PREDETERMINED, SUBSTANTIALLY CONSTANT DIFFERENTIAL BETWEEN THE REFRIGERANT PRESSURE IN SAID FIRST PORTION AND IN A REFERENCE PORTION OF SAID CONTROL LOOP REFLECTING THE SUCTION PRESSURE OF SAID COMPRESSOR; (E) MEANS FOR VARYING THE FLOW OF REFRIGERANT FROM SAID FIRST PORTION INTO A SECOND PORTION OF SAID CONTROL LOOP IN ACCORDANCE WITH VARIATIONS IN CONDITION IN SAID SPACE; (F) REFRIGERANT FLOW RESTRICTION MEANS BETWEEN SAID SECOND PORTION AND SAID REFERENCE PORTION OF SAID CONTROL LOOP; AND, (G) MEANS FOR CONTROLLING THE CONDITIONING OF SAID SPACE INCLUDING CONTROL ACTUATOR MEANS RESPECTIVE TO CHANGES IN THE DIFFERENTIAL IN PRESSURE BETWEEN SAID SECOND PORTION AND SAID REFERENCE PORTION OF SAID CONTROL LOOP. 